JP2018514608A - Star copolymers and their use as viscosity improvers - Google Patents

Abstract

The present invention relates to a star copolymer (C) comprising at least 10% by weight of styrene monomer-derived units and an arm comprising a statistical copolymer (EP) comprising ethylene units and propylene units, and a process for its preparation. The invention also relates to its use in lubricating compositions, in particular its use in lubricating compositions for improving the viscosity index, and thus the resulting lubricating composition, and its use.

Description

  The present invention relates to a viscosity index improver for a lubricating composition, particularly a lubricating composition for a motor vehicle. The present invention more particularly relates to a star copolymer that can be used as a viscosity index improver in a lubricating composition, and thus the resulting lubricating composition that can be used in particular with respect to engine, gearbox or vehicle drive shafts. About.

  The development of engine and engine lubricating composition performance is two sides of the same coin. The more complex the engine design, the greater the optimization of yield and consumption, and the greater the demand for engine lubricating compositions that must improve performance.

  The very high compression inside the engine, in particular the higher piston temperature in the part of the upper piston segment, and the very high temperature in the engine space all lead to an increased demand for lubricating compositions for modern engines.

  The conditions of use of gasoline and diesel engines include both very short trips and long travel distances.

  Also, the oil change interval is most likely to vary from 5000 km for some small diesel engines up to 100,000 km for modern commercial vehicles.

  Lubricating compositions used in these vehicles must therefore have improved levels of performance and performance.

  The formulation of these lubricating compositions also needs to be optimized to reduce energy loss caused by friction inside the engine.

A further essential requirement for engine lubricating compositions relates to environmental aspects. It is practically essential to reduce fuel consumption for the purpose of reducing the consumption of the lubricating composition and in particular CO ₂ emissions.

  The type of vehicle engine lubricant composition affects pollutant emissions and fuel consumption. Vehicle engine lubricating compositions that enable energy savings are often referred to as “fuel eco” compositions (FE).

  The “fuel eco” characteristics of the lubricant need to be as good at low engine speeds as at high engine speeds, since the operating conditions primarily relate to the urban environment with numerous engine shutdowns and restarts. .

  Thus, there is a constant search for energy loss reduction in the field of vehicle lubricants.

  For lubricating compositions for gearboxes or drive shafts, and more generally for lubricating compositions for gearing, these are particularly comfortable driving (perfect gear changes, no noise, trouble-free operation, strong reliability), Assembly life (reduced cold wear, no deposits, extensive thermal stability, safe oiling at high temperatures, stable viscosity, no shear losses, long life), and environmental considerations Many requirements regarding (low fuel consumption, reduced lubricating composition consumption, low noise, easy disposal) must be met. These are requirements placed on lubricating compositions for manual gearboxes and axle gears.

In the motor vehicle sector, the search for reduced CO ₂ emissions requires the development of products that reduce friction in gearboxes and shaft differentials. This reduction in gearbox and shaft differential friction must be obtained for different operating conditions. Such friction reduction should be related to the friction in the lubricating composition, but also to the friction between the gearbox or the differential part of the shaft, in particular the metal part.

  In order to meet these objectives, the viscosity of the lubricating composition is most important. In particular, it is necessary to provide a lubricating composition having a high viscosity index (VI) and a low traction coefficient. The desired lubricating composition should have a high viscosity index that prevents cold start energy loss due to friction and maintains a sufficient lubricating film on the lubricated portion after warm-up. Thus, a high viscosity index ensures a smaller drop in viscosity as the temperature is increased. For this purpose, VI improvers are generally added to lubricating compositions. The purpose of these viscosity modifiers is to ensure selective thickening of the lubricating composition so as to partially offset the drop in viscosity at operating temperature as the temperature increases. These viscosity modifiers are generally polymers, in particular poly (alkyl methacrylate) s, olefin copolymers or hydrogenated styrene / diene copolymers.

  However, these polymers may have insufficient VI, insufficient engine clean performance, mechanical degradation or high cost related to the need to use high contents of these polymers. In addition, these polymer species do not have any particular cold start characteristics or properties.

  Accordingly, there is an interest in providing new VI improvers with high VI and improved cold start characteristics.

  There is also interest in providing new VI improvers with high VIs that do not degrade engine cleanliness.

  There is also an interest in providing new VI modifiers that promote longer engine life and thus less engine friction.

  There is also interest in providing new VI improvers that maintain the properties of lubricating compositions including use under harsh conditions (shear, elongation, slip, etc.).

  There is also interest in providing new VI improvers with mechanical properties that exhibit little degradation over time, regardless of the force applied and the duration of such force.

  There is also interest in providing new VI improvers with high VI that lasts for long periods of time and improved cold start properties.

  There is also interest in providing new VI improvers that reduce the coefficient of friction of lubricating oils.

  There is also an interest in providing VI improvers that can be adsorbed to the lubricated surface, thereby creating desirable film thicknesses for protection of the lubricated surface and friction limitation.

  There is also interest in providing new VI improvers that have the above advantages and that are easy to formulate a lubricating composition.

  There is also interest in providing a lubricating composition that reduces fuel consumption in a vehicle with an engine, drive shaft or gearbox, or vehicle with a transmission.

  There is also interest in providing lubricating compositions having “fuel eco” characteristics at both low and high engine speeds.

  There is also interest in providing a lubricating composition that has “fuel eco” characteristics that are maintained over time, while maintaining rheological and tribological characteristics and ensuring maintained engine cleanliness.

  To meet these objectives, the present invention comprises a statistical copolymer (EP) comprising at least 10% by weight of styrene monomer-derived units and comprising ethylene repeat units (E) and propylene repeat units (P). A star copolymer (C) with arms is proposed.

  Generally, the star copolymer includes a core and arms on the outer edge of the core. Preferably, the star copolymer (C) of the present invention comprises at least 3 arms. Preferably, the star copolymer (C) of the present invention has 3 to 25 arms, preferably 3 to 20 arms, preferably 3 to 15 arms, preferably 3 to 10 arms, such as 4, Includes 5, 6, 7 or 8 arms.

In certain embodiments, the present invention also relates to a star copolymer (C) having an arm comprising an S block and an EP block.
S is a block containing units derived from styrene monomer,
EP is a statistical copolymer comprising ethylene repeat units (E) and propylene repeat units (P);
Copolymer (C) contains at least 10% by weight of styrene monomer-derived units.

  In this particular embodiment, the arm can also include at least one other monomer or at least one other block between block S and block EP.

In the present invention, the arm of the star copolymer (C) preferably has the general formula S-EP (wherein
S is a block containing units derived from styrene monomer,
EP is a statistical copolymer containing ethylene repeat units E and propylene repeat units (P). )
Of copolymers.

Accordingly, the star copolymer (C) is preferably of the general formula S-EP (wherein
S is a block containing units derived from styrene monomer,
EP is a statistical copolymer containing ethylene repeat units (E) and propylene repeat units (P). )
Defined as having an arm comprising a copolymer of
Copolymer (C) contains at least 10% by weight of styrene monomer-derived units.

  It will be understood that the copolymer (EP) of each of the arms can be the same or different.

  It will also be appreciated that the copolymer S-EP for each of the arms can be the same or different.

  Preferably, EP is a statistical copolymer formed with ethylene repeat units and propylene repeat units. Preferably, the EP is a statistical copolymer comprising units derived from ethylene monomer (E) and units derived from propylene monomer (P).

  Preferably, S is a block formed of styrene monomer-derived units.

  Preferably, S is a block formed with units derived from styrene monomers and EP is a statistical copolymer formed with ethylene repeat units (E) and propylene repeat units (P).

  Preferably, S represents a block formed of units derived from styrene monomers, and EP represents a statistical copolymer comprising units E derived from ethylene monomers and units (P) derived from propylene monomers.

  Particularly advantageously, the block S, if present, is arranged at the outer edge of the core of the star copolymer (C) and the copolymer EP is arranged at the end of the arm. Particularly advantageously, the block S of the arm, if present, can participate in the formation of the core of the star copolymer (C) according to the invention.

In certain embodiments of the invention the star copolymer (C) is
A crosslinked core comprising units derived from styrene monomers;
-An arm comprising a statistical copolymer (EP) comprising ethylene repeat units (E) and propylene repeat units (P),
Copolymer (C) contains at least 10% by weight of styrene monomer-derived units.

In certain embodiments of the invention the star copolymer (C) is
A crosslinked core comprising units derived from styrene monomers;
-General formula S-EP (wherein
S is a block containing units derived from styrene monomer,
EP is a statistical copolymer containing ethylene repeat units (E) and propylene repeat units (P). )
An arm comprising a copolymer of
Copolymer (C) contains at least 10% by weight of styrene monomer-derived units.

  The cross-linked core can be obtained by using a cross-linking agent (or coupling agent) of a repeating unit particularly found in the core. The cross-linking agent can be selected in particular from compounds having two non-conjugated alkenyl groups, which can be polyalkenyl, ie aliphatic, aromatic or heterocyclic. In particular, mention may be made of dienes such as divinylbenzene, norbornadiene and the like.

  In one embodiment of the invention, the arm comprising a statistical copolymer (EP) having ethylene repeat units and propylene repeat units is attached by a bond L to a cross-linked core comprising units derived from styrene monomers.

  In certain preferred embodiments of the invention, the bond L is at least one halogen functional group, or one oxygenated functional group such as an ester functional group, an alcohol functional group, an acid functional group, an ether functional group, an epoxide functional group, an acid anhydride. Carbon groups containing product functional groups and derivatives thereof; at least one nitrogen-containing functional group such as an amine functional group, amide functional group, imide functional group; at least one phosphorus-containing functional group such as phosphonic acid functional group A group, a carbon group containing phosphoric acid; a carbon group containing at least one sulfur-containing functional group, for example a sulfonyl group, such as the group alkylene glycol, polyethylene glycol, poly (ethylene-propylene) glycol, poly (ethylene-butylene) glycol Selected.

  In certain more preferred embodiments of the invention, the bond L is selected from at least one halogen functional group, or an epoxide functional group, or a carbon group comprising an acid anhydride functional group, preferably a maleic anhydride functional group. The

  Particularly preferably, the star copolymer (C) of the present invention is 10 to 60% by weight, preferably 10 to 50%, preferably 10 to 40%, preferably 10 to 30%, based on the total weight of the copolymer (C). %, Preferably 20-60%, preferably 20-50%, preferably 20-40%, preferably 20-30%, preferably 15-60%, preferably 15-50%, preferably 15-40% 15-35%, preferably 15-30%, preferably 25-60%, preferably 25-50%, preferably 25-40%, preferably 25-35%, preferably 25-30%, Preferably 30 to 60%, preferably 30 to 50%, preferably 30 to 40%, preferably 30 to 35% of styrene monomer-derived units are included.

  Particularly preferably, the star copolymer (C) of the present invention is derived from 15 to 50% by weight, preferably 20 to 40% by weight, preferably 20 to 30% by weight of styrene monomer, based on the total weight of the copolymer (C). Includes units.

  In the present invention, the expressions “from x to y” and “from x to y” are interpreted to include the boundaries x and y.

  The star copolymer (C) of the present invention has a weight-average molecular weight ( Mw).

  In the star copolymer (C) of the present invention, each of the same or different arms has a weight average molecular weight (Mw) of 25,000 to 300,000 g / mol, preferably 25,000 to 200,000 g / mol, more preferably 25,000 to 100,000 g / mol. .

  In the star copolymer (C) of the present invention, the arms are all the same or different, and the molecular weight average (Mw) of the arms is preferably 25,000 to 300,000 g / mol, preferably 25,000 to 200,000 g / mol, more preferably 25,000 to 100,000 g / mol. mol.

  In the present invention, the weight average molecular weight (Mw) is obtained by gel permeation chromatography (GPC).

  The star copolymer (C) of the present invention is defined as having an arm comprising a statistical ethylene-propylene copolymer (EP copolymer).

  Each EP copolymer of the arms can be the same or different, preferably 14-90% by weight, preferably 30-90%, preferably 40-90%, preferably 50%, based on the total weight of the EP copolymer. -90%, preferably 60-90%, preferably 70-90%, preferably 80-90%, preferably 30-80%, preferably 40-80%, preferably 50-80%, preferably 60- It will be understood that it contains 80%, preferably 70-80% ethylene repeat units.

  Preferably, the EP copolymer of each of the arms can be the same or different and comprises 50-80 wt%, 60-80 wt% ethylene repeat units, based on the total weight of the EP copolymer.

  Preferably, the EP copolymer of each of the arms is the same or different and averages 14 to 90% by weight, preferably 30 to 90%, preferably 40 to 90%, preferably 50, based on the total weight of the EP copolymer. -90%, preferably 60-90%, preferably 70-90%, preferably 80-90%, preferably 30-80%, preferably 40-80%, preferably 50-80%, preferably 60- 80%, preferably 70-80% ethylene repeat units are included.

  Preferably, each EP copolymer of the arms is the same or different and comprises an average of 50-80 wt%, preferably 60-80 wt% ethylene repeat units, based on the total weight of the EP copolymer.

Particularly preferably, the star copolymer (C) of the present invention comprises
Having a weight average molecular weight (Mw) of 90000-1000000 g / mol, for example 90000-800000 g / mol;
-15 to 50% by weight, preferably 20 to 40% by weight, preferably 20 to 30% by weight of styrene monomer-derived units, based on the total weight of the copolymer (C);
Each EP copolymer of the arms is the same or different and contains, on average, 50 to 80% by weight, preferably 60 to 80% by weight of ethylene repeating units, based on the total weight of the EP copolymer; or each of the arms The EP copolymers can be the same or different and comprise 50 to 80% by weight, preferably 60 to 80% by weight of ethylene repeating units, based on the total weight of the EP copolymer.

Particularly preferably, the star copolymer (C) of the present invention comprises
Having a weight average molecular weight (Mw) of 90000-1000000 g / mol, for example 90000-800000 g / mol;
-15 to 50% by weight, preferably 20 to 40% by weight, preferably 20 to 30% by weight of styrene monomer-derived units, based on the total weight of the copolymer (C);
Each EP copolymer of the arms is the same or different and contains, on average, 50 to 80% by weight, preferably 60 to 80% by weight of ethylene repeating units, based on the total weight of the EP copolymer; or each of the arms The EP copolymers can be the same or different and comprise 50-80% by weight, preferably 60-80% by weight, of ethylene repeat units, based on the total weight of the EP copolymer;
Each of the same or different arms has a weight average molecular weight (Mw) of 25000-200000 g / mol, preferably 25000-100000 g / mol; or the arms are all the same or different and the molecular weight average of the arms (Mw ) Is 25,000 to 150,000 g / mol, preferably 25,000 to 100,000 g / mol.

  Particularly advantageously, the inventors have found that the star copolymer C of the present invention has at least one polar group located on at least one of the arms, preferably on the EP portion of the arm, preferably at the end of the EP chain. In addition, it has been found that can be further included. While not wishing to be bound by any theory, the polar groups interact with the surface to be lubricated, thereby improving the adhesion of the copolymer (C) of the present invention and ensuring the presence of a film sufficient for lubrication, Therefore, the lubrication performance can be improved. Polar groups are in particular at least one oxygenated functional group, such as ester functional groups, alcohol functional groups, acid functional groups, ether functional groups, epoxide functional groups, carbon groups including anhydride functional groups, and derivatives thereof; At least one nitrogen-containing functional group, for example a carbon group comprising an amine functional group, an amide functional group, an imide functional group; at least one phosphorus-containing functional group, for example a phosphonic acid functional group, a carbon group comprising a phosphoric acid functional group; at least one It can be selected from two sulfur-containing functional groups such as carbon groups containing sulfonyl, such as the group alkylene glycol, polyethylene glycol, poly (ethylene-propylene) glycol, poly (ethylene-butylene) glycol. Preferably, the polar group is a group

(Q represents the bond of the polar group to the arm of the star copolymer.)
It is.

  The copolymer (C) of the present invention can be in pure form or in the form of a dispersion in an anhydrous medium. The anhydrous medium can in particular be an oil, preferably a base oil. The resulting dispersion can be added to a base oil, particularly as described below, to form a lubricating composition.

  The present invention also relates to a process for preparing the copolymer (C) as described above.

In a first embodiment, the copolymer (C) of the present invention comprises
a) polymerizing a styrene monomer via anionic polymerization in the presence of a crosslinking agent;
b) oligomerizing short butadiene blocks;
c) polymerizing ethylene and propylene monomers on the copolymer obtained in step b) via Ziegler-Natta polymerization, for example in the presence of TiCl ₄ ;
d) optionally hydrogenating the polymer obtained in step c);
e) can be obtained by method P1) comprising the step of recovering the star copolymer (C) of the invention.

In a second embodiment, the copolymer (C) of the present invention comprises
a) preparing ethylene and propylene monomers via Ziegler-Natta polymerization;
b) inactivating the polymer obtained in step a) with an inhibitor, in particular an alcohol type, preferably with reactive functionalization;
c) esterifying the polymer obtained in b);
d) controlled radical polymerization of the polymer obtained in step c) with a styrene monomer and a crosslinking agent;
e) optionally hydrogenating the polymer obtained in step d);
f) It can be obtained by the method (P2) including the step of recovering the star copolymer C of the present invention.

In a third embodiment, the copolymer C of the present invention is
a) preparing the core by controlled radical copolymerization of styrene monomers in the presence of a crosslinking agent;
b) functionalizing the core obtained in step a) via controlled radical polymerization by adding ethylene and propylene monomers;
c) optionally adding a polymerizable polar functional group to the reaction medium obtained in step b);
d) optionally, if applicable, hydrogenating the polymer obtained in step b) or c);
e) It can be obtained by the method (P3) including the step of recovering the star copolymer (C) of the present invention.

  In this particular embodiment, step c) comprises at least one group comprising at least one polar functional group on the copolymer (C), preferably at the end of the chain of the EP copolymer, as defined above. Graft.

In a fourth embodiment, the copolymer (C) of the present invention comprises
a) synthesizing the core via metallocene polymerization of a styrene monomer in the presence of a crosslinking agent;
b) synthesizing an ethylene-propylene copolymer via metallocene polymerization of ethylene and propylene monomers;
c) It can be obtained by the method (P4) including the step of recovering the star copolymer (C) of the present invention.

  In the above method, a person skilled in the art can determine, based on his general knowledge, the amount of monomer used and the specific reaction conditions giving the star copolymer (C) of the present invention.

In a fifth embodiment, the copolymer (C) of the present invention comprises
a) synthesizing ethylene-propylene copolymer EP;
b) synthesizing a compound comprising a counter radical (e.g. selected from nitroxide and xanthate) capable of generating a radical comprising a group comprising at least one polar functional group;
c) reacting the ethylene-propylene copolymer EP obtained in step a) with a compound capable of generating radicals obtained in step b);
d) copolymerizing the copolymer obtained in step c) with a styrene monomer and a crosslinking agent;
e) optionally hydrogenating the polymer obtained in step d);
f) recovering the star copolymer (C) of the present invention comprising at least one group comprising at least one polar functional group, preferably at the end of the chain of the EP copolymer as defined above. (P5).

In a sixth embodiment, the copolymer (C) of the present invention comprises
a) synthesizing a statistical copolymer EP comprising ethylene repeat units, propylene repeat units, and residual double bonds;
b) functionalizing the EP copolymer from step a) with a nucleophilic addition-reactive functional group;
c) polymerizing the styrene monomer in the presence of a crosslinking agent;
d) adding the polymer from step c) to the copolymer EP from step b);
e) It can be obtained by the method (P6) including the step of recovering the star copolymer (C) obtained in step d).

  In one preferred embodiment of the invention, the copolymer (C) is obtained by the method (P6) as defined above.

  In one or more preferred embodiments of the present invention, the nucleophilic addition reactive functional group of step b) is at least one oxygenated functional group such as an ester functional group, an alcohol functional group, an acid functional group, an ether. Functional groups, epoxide functional groups, acid anhydride functional groups, carbon groups containing halogen functional groups, and derivatives thereof; at least one nitrogen-containing functional group, such as carbon groups containing amine functional groups, amide functional groups, imide functional groups At least one phosphorus-containing functional group such as a phosphonic acid functional group, a carbon group containing a phosphoric acid functional group; at least one sulfur-containing functional group such as a carbon group containing sulfonyl such as a group alkylene glycol, polyethylene glycol, poly (ethylene -Propylene) glycol, poly (ethylene-butylene) glycol. Preferably, the reactive functional group is selected from carbon groups including epoxide functional groups, anhydride functional groups, halogen functional groups, advantageously epoxide functional groups, or maleic anhydride functional groups.

  In another preferred embodiment of the invention, the method (P6) comprises step b-1) after step b) and before step c), said step b-1) being derived from step b) A step of purifying the EP copolymer.

  Advantageously, step b-1) is carried out by washing the EP copolymer with methanol followed by solubilization in toluene and evaporation.

  This step is particularly true when the (EP) copolymer is anhydrous and shows no trace of acidity when the nucleophilic addition reactive functional group is selected from among carbon groups containing at least one acid anhydride functional group. Making it particularly possible.

  In another preferred embodiment of the invention, the polymerization of step c) is an anionic polymerization.

  In a more preferred embodiment of the invention, the polymerization of step c) is an anionic polymerization in the presence of a cross-linking agent.

  The cross-linking agent can be selected from all compounds known as cross-linking agents that can be used for anionic polymerization.

  Advantageously, the cross-linking agent is divinylbenzene.

  In another preferred embodiment of the invention, method (P6) comprises step d-1) between step d) and step e), said step d-1) being carried out in a polar solvent in step d ) After which the copolymer obtained is precipitated.

  Advantageously, the polar solvent is methanol.

  The invention also relates to a lubricating composition comprising at least one base oil and at least one star copolymer (C) according to the invention.

  In general, the lubricating composition of the present invention can comprise any type of animal or plant, mineral, synthetic, or natural lubricating base oil known to those skilled in the art.

  The base oil used in the lubricating composition of the present invention is a mineral or synthetic oil (Table A) belonging to the group I to V (or equivalent to these in the ATIEL classification) defined in the API classification or these Can be a mixture of

  The mineral base oil of the present invention is obtained by purification operations such as crude oil environment and vacuum distillation, followed by solvent extraction, desaturation, solvent dewaxing, hydrotreating, hydrocracking, hydroisomerization, and hydrofinishing. All types of base oils that can be used are listed.

  Mixtures of synthetic and mineral oils can also be used.

  In general, the different lubricants that produce the lubricating composition of the present invention, other than the need to have properties of viscosity, viscosity index, sulfur content, and oxidation resistance, which are particularly compatible with engine use or vehicle transport parts. There are no restrictions on the use of sex-based.

The base oil of the lubricating composition of the present invention can also be selected from synthetic oils such as some esters of carboxylic acids and alcohols, and polyalphaolefins. Polyalphaolefins used as base oils are 1.5-15 mm ² .. in accordance with ASTM D445 standard. Obtained from a monomer having a viscosity at 100 ° C. of s ⁻¹ of, for example, 4 to 32 carbon atoms, such as octene or decene. Its molecular weight average is generally between 250 and 3000 according to the ASTM D5296 standard.

  Preferably, the base oil of the present invention is selected from the above base oils having an aromatic content of 0-45%, preferably 0-30%. The aromatic content of the oil is measured according to the UV Burdett method. While not wishing to be bound by any theory, the aromaticity of the base oil is a feature that allows an optimized behavior of the polymer as a function of temperature. The choice of low aromatic oil gives the optimum conditions at the highest temperature.

  Advantageously, the lubricating composition of the present invention comprises at least 50% by weight of base oil, based on the total weight of the composition.

  More advantageously, the lubricating composition of the present invention comprises at least 60 wt.%, And even at least 70 wt.

  Particularly advantageously, the lubricating composition according to the invention comprises from 60 to 99.5% by weight of base oil, preferably from 70 to 99.5% by weight of base oil, based on the total weight of the composition.

  A number of additives can be used in connection with this lubricating composition of the present invention.

  Preferred additives for the lubricating composition of the present invention include cleaning additives, anti-wear additives, friction modifying additives, extreme pressure additives, dispersants, pour point improvers, defoaming additives, thickeners and these. Selected from a mixture of

  Preferably, the lubricating composition of the present invention comprises at least one antiwear additive, at least one extreme pressure additive, or a mixture thereof.

  The antiwear and extreme pressure additives protect the friction surface by forming a protective film adsorbed on the surface.

There are various antiwear additives. Preferably, for the lubricating compositions of the present invention, the antiwear additive is selected from among metal alkylthiophosphates, particularly zinc alkylthiophosphates, particularly zinc dialkyldithiophosphates, ie phosphorous-sulfurized additives such as ZnDTPs. Preferred compounds of the formula Zn ((SP (S) ( OR 1) (OR 2)) 2 ( wherein the same or different R ¹ and R ² are each independently an alkyl group, preferably of 1 to 18 An alkyl group having a carbon atom).

  Amine phosphates are also antiwear additives that can be used in the lubricating compositions of the present invention. However, the phosphorus contributed by these additives may act as a poison for the catalyst system of the motor vehicle because these additives produce ash. These effects can be minimized by partially substituting the amine phosphate with polysulfides, such as, in particular, phosphorus-free additives such as sulfurized olefins.

  Advantageously, the lubricating composition of the present invention is 0.01 to 6% by weight, preferably 0.05 to 4% by weight, more preferably 0.1 to 2% by weight, based on the total weight of the lubricating composition. Antiwear and extreme pressure additives.

  Advantageously, the lubricating composition of the present invention may comprise at least one friction modifying additive. The friction modifying additive can be selected from among metal elements and compounds that provide ash-free compounds. Among the compounds that provide metal elements, mention is made of transition metal complexes, such as Mo, Sb, Sn, Fe, Cu, Zn, etc., whose ligands can be hydrocarbon compounds containing oxygen, nitrogen, sulfur or phosphorus atoms. be able to. Ash-free friction modifying additives are generally of organic origin and are fatty acids and polyols, alkoxylated amines, alkoxylated aliphatic amines, aliphatic epoxides, monoesters of borate aliphatic epoxides; aliphatic amines, or fatty acid glycerol esters Can be selected from. According to the invention, the aliphatic compound comprises at least one hydrocarbon group having 10 to 24 carbon atoms. Advantageously, the lubricating composition of the present invention is 0.01-2% by weight, or 0.01-5% by weight, preferably 0.1-1.5% by weight, based on the total weight of the lubricating composition. Or 0.1-2% by weight of a friction modifying additive.

  Advantageously, the lubricating composition of the present invention may comprise at least one antioxidant additive.

  Antioxidant additives generally delay the deterioration of the lubricating composition during use. This degradation may translate in particular as deposit formation, as the presence of sludge, or as an increase in the viscosity of the lubricating composition.

Antioxidant additives act in particular as radical inhibitors or hydroperoxide decomposers. Among the commonly used antioxidants, mention may be made of phenolic antioxidant additives, amino antioxidants, phosphorus-sulfurized antioxidant additives. Some of these antioxidant additives, such as phosphorus-sulfurized antioxidant additives, may produce ash. The phenolic antioxidant additive can be ash-free or can be in the form of a neutral or basic metal salt. Antioxidant additives, in particular, sterically hindered phenols, sterically hindered phenols esters, and sterically hindered phenols containing thioethers bridge, diphenylamine, diphenylamine substituted with at least one C ₁ -C ₁₂ alkyl group, N, N It can be selected among '-dialkyl-aryl-diamines and mixtures thereof.

Preferably, according to the present invention, the sterically hindered phenol is such that at least one adjacent carbon of the carbon having an alcohol functional group is at least one C ₁ -C ₁₀ alkyl group, preferably a C ₁ -C ₆ alkyl group, It is preferably selected from compounds containing a phenol group substituted by a C ₄ alkyl group, preferably substituted by a tert-butyl group.

Amino compounds are another class of antioxidant additives that can optionally be used in combination with phenolic antioxidant additives. Examples of amino compounds are aromatic amines, such as the formula NR ³ R ⁴ R ⁵ , wherein R ³ is an aliphatic or aromatic group, optionally substituted, and R ⁴ is an aromatic group. And optionally substituted, R ⁵ is a hydrogen atom, an alkyl group, an aryl group, or a formula R ⁶ S (O) _z R ⁷ , wherein R ⁶ is an alkylene group or an alkenylene group, R ⁷ is an alkyl group, an alkenyl group or an aryl group, and z is 0, 1 or 2.))).

  Sulfurized alkylphenols or their alkali metal salts or alkaline earth metal salts can also be used as antioxidant additives.

  Another class of antioxidant additives are those of copper compounds such as copper thio- or dithio-phosphates, copper and carboxylates, copper dithiocarbamates, sulfonates, phenates and acetylacetonates. Copper I and II salts, succinic acid or anhydride salts can also be used.

  The lubricating composition of the present invention can contain any kind of antioxidant additives known to those skilled in the art.

  Advantageously, the lubricating composition comprises at least one ash-free antioxidant additive.

  Also advantageously, the lubricating composition of the present invention comprises 0.5-2% by weight of at least one antioxidant additive, based on the total weight of the composition.

  The lubricating composition of the present invention can also include at least one cleaning additive.

  The cleaning additive generally reduces the formation of deposits on the surface of the metal part by dissolving secondary oxidation and combustion products.

  Cleaning additives that can be used in the lubricating compositions of the present invention are generally known to those skilled in the art. The cleaning additive can be an anionic compound containing a long lipophilic hydrocarbon chain and a hydrophilic head. The related cation can be a metal cation of an alkali metal or alkaline earth metal.

  The cleaning additive is preferably selected from alkali metal or alkaline earth metal salts of carboxylic acids, sulfonates, salicylates, naphthenates, and phenate salts. The alkali metal or alkaline earth metal is preferably calcium, magnesium, sodium or barium.

  These metal salts generally contain a stoichiometric amount or excess, ie, an amount greater than the stoichiometric amount of metal. It is therefore an overbased detergent additive; excess metal that renders the detergent additive overbased is therefore generally in the form of metal salts that are insoluble in oils, such as carbonates, hydroxides, oxalates, acetates, glutamates, preferably Is carbonate.

  Advantageously, the lubricating composition of the present invention may comprise from 2 to 4% by weight of cleaning additive, based on the total weight of the lubricating composition.

  Also advantageously, the lubricating composition of the present invention may additionally comprise at least one pour point dispersion additive.

  By showing the formation of paraffin crystals, pour point dispersants generally improve the behavior of the lubricating compositions of the present invention at cold temperatures.

  As examples of pour point dispersion additives, mention may be made of alkyl polymethacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalenes, alkylated polystyrenes.

  Advantageously, the lubricating composition of the present invention may also include at least one dispersant.

  The dispersant can be selected from Mannich base, succinimide, and derivatives thereof.

  Also advantageously, the lubricating composition of the present invention may comprise 0.2 to 10% by weight of a dispersant relative to the total weight of the lubricating composition.

  The lubricating composition can also include at least one additional polymer that improves the viscosity index. As examples of additional polymers that improve the viscosity index, mention may be made of polymer esters, homopolymers or copolymers, hydrogenated or non-hydrogenated styrene, butadiene, and isoprene, polymethacrylate (PMA).

  The lubricating composition of the present invention can be in different forms. In particular, the lubricating composition of the present invention can be an anhydrous composition. Preferably, the lubricating composition is not an emulsion.

  The lubricating composition according to the invention is preferably 0.1 to 50% by weight, preferably 0.5 to 30% by weight of the star copolymer (C) as defined above, relative to the total weight of the lubricating composition. including.

  Preferably, for use in engines, the lubricating composition of the present invention is defined above in an amount of 0.1 to 10% by weight, preferably 0.5 to 5% by weight, based on the total weight of the lubricating composition. Such a star copolymer C.

  Preferably, for use in transmission parts, the lubricating composition of the present invention is 5 to 50% by weight, preferably 10 to 30% by weight of the star as defined above, relative to the total weight of the lubricating composition. Copolymer (C) is included.

  The invention also relates to the use of the copolymer (C) according to the invention as a viscosity index improver for lubricating compositions. Preferably, the use of the copolymer (C) of the present invention allows a viscosity index of at least 200 to be achieved. Viscosity index is measured according to ASTM D2270 or ISO standards.

  Preferably, the copolymer (C) is used in a proportion of 0.1 to 50% by weight, preferably 0.5 to 30% by weight, based on the total weight of the lubricating composition.

  Preferably, for use in engines, copolymer C is used in a proportion of 0.1 to 10% by weight, preferably 0.5 to 5% by weight, based on the total weight of the composition.

  Preferably, for use in the transmission part, copolymer C is used in a proportion of 0.1 to 50% by weight, preferably 0.5 to 30% by weight, based on the total weight of the composition.

  The ranges given above apply to pure copolymers or dispersions of copolymers in anhydrous media as defined above.

The present invention
-To reduce the coefficient of friction of the lubricating composition; or-in the lubricating composition, to reduce fuel consumption of an engine, in particular a motor vehicle engine; or-in the lubricating composition, provided with a drive shaft or gearbox To reduce the fuel consumption of the vehicle; or to reduce the fuel consumption of the vehicle with the transmission in the lubricating composition; or to reduce the traction coefficient of the lubricating composition, particularly with respect to the transmission or gearbox Or the use of copolymer C as defined above for improving the fuel eco (FE) of a lubricating composition.

  Preferably, the copolymer (C) is used in a proportion of 0.1 to 50% by weight, preferably 0.5 to 30% by weight, based on the total weight of the lubricating composition.

  Preferably, for use in engines, the copolymer (C) is used in a proportion of 0.1 to 10% by weight, preferably 0.5 to 5% by weight, based on the total weight of the composition.

  Preferably, for use in transmission, the copolymer (C) is used in a proportion of 0.1 to 50% by weight, preferably 0.5 to 30% by weight, based on the total weight of the composition.

  The ranges given above apply to pure copolymers or dispersions of copolymers in anhydrous media as defined above.

The present invention
-To reduce fuel consumption of engines, in particular motor vehicle engines; or-to reduce fuel consumption of vehicles with driveshafts or gearboxes; or-to reduce fuel consumption of vehicles with transmissions Also relates to the use of a lubricating composition as defined above.

  The invention also relates to a method for improving the viscosity index of a lubricating composition, comprising the addition of a star copolymer (C) according to the invention to the lubricating composition.

  In this method, the copolymer (C) is used in a proportion of 0.1 to 50% by mass, preferably 0.5 to 30% by mass, based on the total mass of the lubricating composition.

  Preferably, for use in engines, the copolymer (C) is used in a proportion of 0.1 to 10% by weight, preferably 0.5 to 5% by weight, based on the total weight of the composition.

  Preferably, for use in transmission, copolymer C is used in a proportion of 0.1 to 50% by weight, preferably 0.5 to 30% by weight, based on the total weight of the composition.

  The ranges given above apply to pure copolymers or dispersions of copolymers in anhydrous media as defined above.

The present invention
-Reduce the coefficient of friction of the lubricating composition; or-reduce the fuel consumption of an engine, in particular a motor vehicle engine; or-reduce the fuel consumption of a vehicle with a drive shaft or gearbox; or-comprise a transmission Reducing the traction coefficient of a lubricating composition, particularly with respect to transmissions or gearboxes; or-improving the fuel economy (FE) of a lubricating composition comprising:
It also relates to a process comprising the addition of a star copolymer C of the present invention to the lubricating composition, or to a lubricating composition used in the engine or the vehicle.

  In this process, the copolymer C is used in a proportion of 0.1 to 50% by weight, preferably 0.5 to 30% by weight, based on the total weight of the lubricating composition.

  Preferably, for use in engines, copolymer C is used in a proportion of 0.1 to 10% by weight, preferably 0.5 to 5% by weight, based on the total weight of the composition.

  Preferably, for use in transmission, copolymer C is used in a proportion of 0.1 to 50% by weight, preferably 0.5 to 30% by weight, based on the total weight of the composition.

  The ranges given above apply to pure copolymers or dispersions of copolymers in anhydrous media as defined above.

The present invention
-Reducing fuel consumption in an engine, in particular a motor vehicle engine; or-reducing fuel consumption in a vehicle with a drive shaft or gearbox; or-reducing fuel consumption in a vehicle with a transmission, comprising: It also relates to a method comprising the use of the lubricating composition of the present invention.

  By analogy, in particular, the advantageous or preferred characteristics of the star copolymer (C) of the invention or the lubricating composition of the invention define the particular advantageous or preferred use of the invention.

  The invention will be described using non-limiting examples.

Example 1 Preparation of Star Copolymer (C) of the Invention The entire preparation process is carried out in a controlled nitrogen atmosphere. All monomers are purified on a neutral active aluminum oxide column and stored with 4A molecular sieves in an inert atmosphere. The solution of sec-BuLi used is 1.4M (in hexane).

  To a 2 L reactor equipped with a mechanical agitator (anchor type) and counter blade, 500 mL anhydrous toluene (purified by azeotropy), 1.0 mL styrene (8.7 mmol) and 1.20 mL N, N, N ′ , N′-tetramethylethylenediamine (4.0 mmol) is added. The resulting solution is degassed by three vacuum / nitrogen cycles and cooled to −20 ° C. with stirring (200 rpm). Proton impurities are neutralized by the dropwise addition of sec-butyllithium until persistent orange / yellow coloration is obtained (the amount of sec-BuLi varies from 0.2 to 0.6 mL). The sec-BuLi addition is then added rapidly with stirring at 350 rpm (2.85 mL, 4 mmol) followed by 1.12 mL divinylbenzene (8 mmol). The medium quickly becomes dark red colored. The medium is left under 30 minutes of stirring (200 rpm) at −20 ° C. Styrene (15 mL, 130 mmol) is then rapidly added at −20 ° C. The medium is heated to 50 ° C. for 2 hours and then lowered to ambient temperature (the color of the medium is light orange). A solution of statistical ethylene / propylene copolymer containing anhydrous maleic functionality (V4021, distributed by FUNCTIONAL PRODUCTS INC, hereinafter referred to as OCP / MAH) is added to the medium using a cannula in an inert atmosphere.

  Prior to addition, OCP / MAH is purified by the following method: 30 g OCP / MAH is solubilized in 500 mL toluene in a round bottom flask equipped with mechanical agitation. The copolymer is dissolved in 16 hours under vigorous stirring at 35 ° C. The copolymer is then precipitated in 1.5 L of MeOH under vigorous stirring. The solid is washed with 500 mL additional methanol by grinding. The solid is then dried under reduced pressure at 40 ° C. for 4 hours.

  The obtained OCP / MAH (28.5 g) is dissolved in 700 mL of toluene. The resulting solution is placed in a Dean-Stark type assembly under nitrogen reflux for 24 hours with regular discharge of the toluene / water binary system in the Dean-Stark apparatus. The solution is then cooled to ambient temperature for IR analysis.

  The addition is stopped as soon as the orange color has completely disappeared (pale yellow medium) (75% by volume solution, ie 21 g OCP). 20 mL of methanol is added to quench the reaction. The resulting copolymer is purified by precipitation and washed by grinding in 2 L of methanol. The copolymer is vacuum dried overnight at ambient temperature.

  The resulting copolymer (C) is a star copolymer comprising 34% by weight of styrene repeat units (measured by NMR spectroscopy) and an arm comprising a statistical ethylene / propylene copolymer.

Example 2: Evaluation of viscosity index to improve the properties of the inventive star copolymer (C) The star copolymer of Example 1 was solubilized in the following base oil:
Base oil 1: Group I base oil (ISO standard: dynamic viscosity measured at 100 ° C. according to 3104: = 5.19 mm ² / s)
Base oil 2: alkyl naphthalene type group V base oil (Synthetic 5 sold by Exxonobibil)

  For solubilization, 1 g of the star copolymer of Example 1 was solubilized in 100 g of base oil and stirred on a magnetic hot plate at 150 ° C. for 96 hours.

  Each mixture was then filtered and centrifuged.

  The prepared mixtures 1 and 2 are therefore listed in Table I (the values given correspond to the weight percent).

  The viscosity index of mixtures 1 and 2 and base oils 1 and 2 was measured according to ISO standard 2909. The results are given in Table II.

  These results indicate that the star copolymer (C) of the present invention improves the viscosity index of the base oil regardless of the type of base oil.

  These results thus show that the star copolymers of the present invention can be used in lubricating compositions as VI improvers.

These results thus show that the star copolymers of the present invention can be used in lubricating compositions as VI improvers.
The present disclosure also includes:
[1]
A star copolymer (C) comprising at least 10% by weight of styrene monomer-derived units and having an arm comprising a statistical copolymer (EP) comprising ethylene repeat units and propylene repeat units.
[2]
General formula S-EP (wherein
S is a block containing units derived from styrene monomers;
EP is a statistical copolymer containing ethylene repeat units and propylene repeat units. )
Having an arm comprising a copolymer of
The copolymer (C) according to embodiment 1, comprising at least 10% by weight of styrene monomer-derived units.
[3]
A crosslinked core comprising units derived from styrene monomers;
An arm comprising a statistical copolymer (EP) comprising ethylene repeat units (E) and propylene repeat units (P);
Including
The copolymer (C) according to embodiment 1, comprising at least 10% by weight of styrene monomer-derived units.
[4]
The copolymer according to embodiment 2, wherein the block S of the S-EP copolymer is arranged at the edge at the outer edge of the core and the EP copolymer.
[5]
10-60% by weight, preferably 10-50%, preferably 10-40%, preferably 10-30%, preferably 20-60%, preferably 20-50%, based on the total weight of the copolymer (C). %, Preferably 20-40%, preferably 20-30%, preferably 15-60%, preferably 15-50%, preferably 15-40%, preferably 15-35%, preferably 15-30% , Preferably 25-60%, preferably 25-50%, preferably 25-40%, preferably 25-35%, preferably 25-30%, preferably 30-60%, preferably 30-50%, The star copolymer (C) according to any one of the above aspects 1 to 4, preferably comprising 30 to 40%, preferably 30 to 35% of styrene monomer-derived units.
[6]
The star copolymer (C) according to any one of the above aspects 1 to 5, having a weight average molecular weight (Mw) of 90000 to 15000000 g / mol, preferably 90000 to 1000000 g / mol, for example 90000 to 800000 g / mol.
[7]
3 to 25 arms, preferably 3 to 20 arms, preferably 3 to 15 arms, preferably 3 to 10 arms, preferably 4, 5, 6, 7 or 8 arms Preferably, the arms are the same or different, and the star copolymer (C) according to any one of the above aspects 1 to 6.
[8]
The star copolymer (C) according to any of the above embodiments 1 to 7, wherein each of the same or different arms has a weight average molecular weight (Mw) of 25,000 to 300,000 g / mol, preferably 25,000 to 100,000 g / mol.
[9]
The star copolymer (C) according to any one of the above aspects 1 to 8, wherein the arms are all the same or different, and the molecular weight average (Mw) of the arms is 25,000 to 300,000 g / mol, preferably 25,000 to 100,000 g / mol. .
[10]
The EP copolymer in each of the arms is the same or different and is 14 to 90% by weight, preferably 30 to 90%, preferably 40 to 90%, preferably 50 to 90%, based on the total weight of the EP copolymer, Preferably 60-90%, preferably 70-90%, preferably 80-90%, preferably 30-80%, preferably 40-80%, preferably 50-80%, preferably 60-80%, preferably The star copolymer (C) according to any one of the above aspects 1 to 9, which comprises 70 to 80% ethylene repeating units.
[11]
The EP copolymers in each of the arms are all the same or different and average 14 to 90% by weight, preferably 30 to 90%, preferably 30 to 90%, preferably 40 to 90%, based on the average weight of the EP copolymer. %, Preferably 50-90%, preferably 60-90%, preferably 70-90%, preferably 80-90%, preferably 30-80%, preferably 40-80%, preferably 50-80% The star copolymer (C) according to any one of the above aspects 1 to 9, comprising 60 to 80%, preferably 70 to 80%, of ethylene repeating units.
[12]
Any of the above embodiments 1-11, further comprising at least one group comprising at least one polar functional group located on at least one of the arms, preferably on the EP portion of the arm, preferably at the end of the arm chain. The star copolymer (C) described in 1.
[13]
The star copolymer (C) according to any of the above embodiments 1 to 12, which is in the form of a dispersion in an anhydrous medium, preferably in oil.
[14]
A lubricating composition comprising at least one base oil and at least one star copolymer (C) according to any one of Embodiments 1 to 13.
[15]
15. The embodiment 14 above, comprising 0.1-50% by weight, preferably 0.5-30% by weight of the star copolymer (C) of any of the above embodiments 1-13, based on the total weight of the composition. Lubricating composition.
[16]
Use of the star copolymer (C) according to any one of the above embodiments 1 to 13 as a viscosity index improver for a lubricating composition.
[17]
Use according to aspect 16, wherein the star copolymer (C) is used in a proportion of 0.1 to 50% by weight, preferably 0.5 to 30% by weight, based on the total weight of the composition.
[18]
-To reduce the coefficient of friction of the lubricating composition; or
-In a lubricating composition, to reduce fuel consumption of engines, in particular motor vehicle engines; or
-To reduce fuel consumption of vehicles with drive shafts or gearboxes in lubricating compositions; or
-In a lubricating composition, to reduce the fuel consumption of a vehicle with a transmission; or
-To reduce the traction coefficient of the lubricating composition, especially with respect to transmission parts or gearboxes; or
-To improve the fuel economy (FE) of lubricating compositions
Use of the star copolymer (C) according to any one of the above aspects 1 to 13.
[19]
-To reduce fuel consumption of engines, in particular motor vehicles, or
-To reduce fuel consumption of vehicles with drive shafts or gearboxes; or
-To reduce fuel consumption of vehicles with transmissions
Use of the lubricating composition according to aspect 14 or 15 above.
[20]
a) synthesizing a statistical copolymer (EP) comprising ethylene repeat units, propylene repeat units, and residual double bonds;
b) functionalizing the copolymer (EP) from step a) with a nucleophilic addition-reactive functional group;
c) polymerizing the styrene monomer in the presence of a crosslinking agent;
d) adding the polymer from step c) on top of the copolymer (EP) from step b);
e) recovering the star copolymer (C) obtained in step d)
A method for preparing a star copolymer according to any one of the above aspects 1 to 13, comprising:

Claims (20)

  A star copolymer (C) comprising at least 10% by weight of styrene monomer-derived units and having an arm comprising a statistical copolymer (EP) comprising ethylene repeat units and propylene repeat units. General formula S-EP (wherein
S is a block containing units derived from styrene monomers;
EP is a statistical copolymer containing ethylene repeat units and propylene repeat units. )
Having an arm comprising a copolymer of
2. Copolymer (C) according to claim 1, comprising at least 10% by weight of styrene monomer-derived units. A crosslinked core comprising units derived from styrene monomers;
-An arm comprising a statistical copolymer (EP) comprising ethylene repeat units (E) and propylene repeat units (P),
2. Copolymer (C) according to claim 1, comprising at least 10% by weight of styrene monomer-derived units.   The copolymer according to claim 2, wherein the block S of the S-EP copolymer is arranged at the edge and at the outer edge of the EP copolymer.   10-60% by weight, preferably 10-50%, preferably 10-40%, preferably 10-30%, preferably 20-60%, preferably 20-50%, based on the total weight of the copolymer (C). %, Preferably 20-40%, preferably 20-30%, preferably 15-60%, preferably 15-50%, preferably 15-40%, preferably 15-35%, preferably 15-30% , Preferably 25-60%, preferably 25-50%, preferably 25-40%, preferably 25-35%, preferably 25-30%, preferably 30-60%, preferably 30-50%, Star copolymer (C) according to any one of claims 1 to 4, comprising preferably 30 to 40%, preferably 30 to 35% of styrene monomer derived units.   Star copolymer (C) according to any one of claims 1 to 5, having a weight average molecular weight (Mw) of 90000-15000000 g / mol, preferably 90000-1000000 g / mol, for example 90000-800000 g / mol.   3 to 25 arms, preferably 3 to 20 arms, preferably 3 to 15 arms, preferably 3 to 10 arms, preferably 4, 5, 6, 7 or 8 arms And preferably the arms are the same or different, the star copolymer (C) according to any one of claims 1-6.   The star copolymer (C) according to any one of claims 1 to 7, wherein each of the same or different arms has a weight average molecular weight (Mw) of 25000 to 300000 g / mol, preferably 25000 to 100000 g / mol. .   The star copolymer according to any one of claims 1 to 8, wherein the arms are all the same or different, and the molecular weight average (Mw) of the arms is 25,000 to 300,000 g / mol, preferably 25,000 to 100,000 g / mol. C).   The EP copolymer in each of the arms is the same or different and is 14 to 90% by weight, preferably 30 to 90%, preferably 40 to 90%, preferably 50 to 90%, based on the total weight of the EP copolymer, Preferably 60-90%, preferably 70-90%, preferably 80-90%, preferably 30-80%, preferably 40-80%, preferably 50-80%, preferably 60-80%, preferably The star copolymer (C) according to any one of claims 1 to 9, which comprises 70 to 80% ethylene repeating units.   The EP copolymers in each of the arms are all the same or different and average 14 to 90% by weight, preferably 30 to 90%, preferably 30 to 90%, preferably 40 to 90%, based on the average weight of the EP copolymer. %, Preferably 50-90%, preferably 60-90%, preferably 70-90%, preferably 80-90%, preferably 30-80%, preferably 40-80%, preferably 50-80% The star copolymer (C) according to any one of claims 1 to 9, comprising 60 to 80%, preferably 70 to 80% ethylene repeating units.   12. The method of claim 1, further comprising at least one group comprising at least one polar functional group disposed on at least one of the arms, preferably on the EP portion of the arm, preferably at the end of the arm chain. The star copolymer (C) according to item 1.   13. Star copolymer (C) according to any one of claims 1 to 12, which is in the form of a dispersion in an anhydrous medium, preferably in oil.   Lubricating composition comprising at least one base oil and at least one star copolymer (C) according to any one of the preceding claims.   15. The star copolymer (C) according to any one of claims 1 to 13, comprising 0.1 to 50% by weight, preferably 0.5 to 30% by weight, based on the total weight of the composition. The lubricating composition described in 1.   Use of the star copolymer (C) according to any one of claims 1 to 13 as a viscosity index improver of a lubricating composition.   Use according to claim 16, wherein the star copolymer (C) is used in a proportion of 0.1 to 50% by weight, preferably 0.5 to 30% by weight, based on the total weight of the composition. -To reduce the coefficient of friction of the lubricating composition; or-in the lubricating composition, to reduce the fuel consumption of an engine, in particular a motor vehicle engine; or-in the lubricating composition, provided with a drive shaft or gearbox To reduce vehicle fuel consumption; or-to reduce the fuel consumption of a vehicle with a transmission in the lubricating composition; or-to reduce the traction coefficient of the lubricating composition, particularly with respect to the transmission part or gearbox Or the use of the star copolymer (C) according to any one of claims 1 to 13 for improving the fuel economy (FE) of the lubricating composition. -To reduce fuel consumption of engines, particularly motor vehicle engines; or-to reduce fuel consumption of vehicles with drive shafts or gearboxes; or-to reduce fuel consumption of vehicles with transmissions Use of a lubricating composition according to claim 14 or 15. a) synthesizing a statistical copolymer (EP) comprising ethylene repeat units, propylene repeat units, and residual double bonds;
b) functionalizing the copolymer (EP) from step a) with a nucleophilic addition-reactive functional group;
c) polymerizing the styrene monomer in the presence of a crosslinking agent;
d) adding the polymer from step c) on top of the copolymer (EP) from step b);
The method for preparing a star copolymer according to any one of claims 1 to 13, comprising a step of e) recovering the star copolymer (C) obtained in step d).